Added missing checkout, cache, and Xcode selection steps in integrati…

…on tests job

[ci skip]

.github/workflows/build.yml

@@ -68,6 +68,15 @@ jobs:
         - name: WebDAV
           scheme-name: WebDAVIntegrationTests
     steps:
+      - uses: actions/checkout@v4
+      - uses: actions/cache@v4
+        with:
+          path: .build
+          key: ${{ runner.os }}-spm-${{ hashFiles('**/Package.resolved') }}
+          restore-keys: |
+            ${{ runner.os }}-spm-
+      - name: Select Xcode 15.3
+        run: sudo xcode-select -s /Applications/Xcode_15.3.app
       - name: Run integration tests
         run: set -o pipefail && env NSUnbufferedIO=YES xcodebuild -scheme '${{ matrix.scheme-name }}' -destination "name=$DEVICE" -derivedDataPath $DERIVED_DATA_PATH test | xcpretty
         env: